fix(conversations): accept configuration update items

[skamenan7]

Summary

Refresh the pinned OpenAI specification snapshot and generated conversation item contracts to recognise configuration_update items. This also updates the generated conformance artifacts.

Related issue

Closes #1140

What changed

• configuration_update items now accepted in input/output unions for Conversations.
• Conversation item contracts regenerated from the current OpenAI spec.
• Conformance report updated; 8 response_drift fingerprints (all responses.deleted) are new from the spec refresh and expected.

Validation

• Added Rust contract and conversation handler tests.
• Added an OpenAI SDK integration round-trip test.
• CI conformance check currently reports 8 new fingerprints; these are acknowledged expected changes from the spec refresh.

Checklist

• User-facing behavior and generated documentation are updated.

Breaking changes

None.

[skamenan7]

Hi @leseb, CI is green everywhere except the conformance check. The gate reads ALLOW_NEW_FAILURES from the conformance-failure-acknowledged label, and I cannot apply it myself (no triage perms on the repo). Could you please drop that label on the PR when you get a sec? It retriggers the workflow with --allow-new-failures and the check should go green.